Distance measuring system



ug- 6 17946- w. J. B RowN ETAL 2,405,134

DISTANCE MEASURING SYSTEM Filed Aug. 3, 1942 2 Sheets-Sheet 2 PatentedAug. 6, 1946 UNHTE. STATS TENT OFFHCE DISTANCE lVlEASURING SYSTEMApplication August 3, 1942, Serial No. 453,460

7 Claims.

This invention relates to distance measuring systems and, moreparticularly, to methods of and apparatus for depth finding and for theloeating of distant underwater objects such as submarines and the like.

It has been proposed heretofore to project a beam of energy toward adistant invisible object and to utilize the reflection thereof in suchmanner as to give an indication of the bearing and distance away of saidobject. For that purpose, radio waves, light waves and compressionalwaves at supersonic frequencies have been advocated and tried, thelatter being especially applicable to the locating of objects underWater.

Some success has been attained by transmitting compressional waves, at afixed supersonic frequency, in successive discrete pulses and noting thetime elapsing between the transmission of a pulse and the reception ofthe echo thereof. The pulse system, however, cannot be entirely reliablebecause many spurious echoes are received from objects, both nearby anddistant, that seriously interfere with the recognition and segregationof echoes from objects of the type being searched for. That is aninherent disadvantage of many other known systems and one which had notbeen overcome satisfactorily before the present invention. In additionto discrete spurious echoes, recurrent echoes, resulting fromreverberation, usually cause interference when underwater pulse systemsare employed.

Also, the signal-to-noise ratio with heretofore known supersonic beamsystems of the pulse type has not been satisfactory.

It is, accordingly, an object of this invention to provide a distancemeasuring or depth-finding system, utilizing compressional waves atsupersponic frequencies, that shall be substantially free from thedefects hereinabove enumerated.

Another object of the invention is to provide a distance measuringsystem, of the type described, that shall be capable of providing acontinuous audible or visible indication of the distance to a reflectingbody or surface.

Another object of the invention is to provide a, system of the echo typethat shall be capable of giving a continuous indication of the presenceof an object located at a definite distance away from the sending andreceiving apparatus.

Another object of the invention is to provide a system of the typedescribed that may be pre-set to give indications of objects at adefinite distance therefrom while being substantially immune to spuriousechoes arising from reflecting surfaces at other distances.

Another object of the invention is to provide a system of the typedescribed, having an improved signal-to-noise ratio and thereforecapable of operating under adverse conditions of local interteringnoise. Y

Another object of the invention is to provide a system of the typedescribed that lends itself particularly well to rapid scanning orsearching in the general direction in which the presence of objects suchas submarines is suspected.

Another'object of the invention is to provide system, of the typedescribed, whereby measurements may be so continuously taken of thedistance to an object, such as a submarine or the like, that relativemovement of the object toward or away from the observer may be madeapparent and the speed of movement estimated.

A still further and more specific objecty of the invention is to providea system of the `type described that shall require minimum adjustmentand balancing during utilization thereof.

In accordance with the invention, the echo principle is employed, butmeans are provided whereby a substantially continuous variable fre`quency supersonic exploring wave train is transmitted in the generaldirection of the reflecting object and, if the object is located at thedistance for which the system is adjusted, a Continous distinctivesignal is produced from the echo. The system may be pre-set to explore aregion at a definite radial distance from the transmitterand receiverand to substantially ignore echoes from objects nearer or farther away.

In one embodiment of the invention, an'underwater supersoniccompressional wave is radiated by a directional piezoelectric transduceror the like. The directional pattern may be sharp or broad. Thefrequency of the transmitted'wave is caused to vary periodically andlinearly with respect to time between fixed upper fand lower limits. Adirectional supersonic receiver is provided, the tuning of which also iscaused periodically to vary linearly at the same rate as the tuning ofthe transmitter and over the same range. The tuning 'cycle of thereceiver, however, vis caused to lag the tuning cycle of the transmitterby a controllable and observable time interval and it accepts only thosesignals that have required the said timeV interval to go out to and bereflected back from a remote object.

The receiver may be of the superheterodyne type and the tuning of theheterodyne oscillator may be caused periodically to vary linearly overits range in step with the tuning of the receiver, whereby the echo froman object at the distance for which the system is adjusted produces acontinuous beat note.

In the embodiment just referred to, the tuning of the transmitter, thereceiver and the local 0scillator may be accomplished, for example,through utilization of means such as three variable tuning capacitorsthat are caused to rotate at the same angular velocity. There are anumber of ways by which the tuning of the receiver and local oscillatormay both be caused to lag a controllable time interval behind the tuningof the transmitter. For example, a common shaft may be utilized for therotors of the three condensers. In that case, the shaft could be drivenby a variable speed motor, the lag then being a function of the speed.Alternatively, the speed ofthe shaft could be kept constant, and theangular position of the stator ofthe transmitter tuning capacitor couldbe adjusted with respect to the stators of the other two capacitors.Additionalmodications will be quite obvious to those familiar vwithradio design.

In the preferredembodiment of the invention, however, electronic insteadof mechanical. means are employed for causing the frequency of thetransmitted compressional wave to periodically vary linearly between theupper and lower limits and an electrical Wave corresponding to and inphase with the compressional wave is utilized for the purpose-ofheterodyning the echo in the re- ,f

v trating a preferred embodiment of the invention,

Figure 2 is a circuit diagram illustrating a detail of: the system shownin Fig-ure l,

Figure 3. Vis a composite graph illustrative of. the Inode of operationof the` system exemplified by Figure; 1,V

Figure 4 is a conventionalized diagrammatic view to which referencewill. be, made in the explanation of an alternative embodiment of theinvention, and

Figure. is a compositiva graph illustrative of the mode of operation of.alternativel embodiments ofthe invention described withreference toFigure 4.

Referring now to Figure 1 of the drawings, a preferred embodiment of theinvention includes a transmitting amplifier I that supplies alternatingpotential or current to an underwater transducer or compressionalwave-propagating device 3Y which, for purposes of convenience, will becalledfaradiator. The radiator 3 may be of any well-known type capableof operation at supersonic frequencies, comprising a diaphragm or theVlike.- and piezoelectric, magnetostrictive or other means for impartingvibratory movement thereto. Y Y -V An underwater microphone 5" isalsoprovided, for thepurpose of translating the received echo intoelectric currents orpotentials representative thereof and receivermeans, indicated generally by the dotted rectangle l', arev connectedtov the output terminals thereof for renderingsuch'electricalcurrents orpotentials observable. The speciiic construction of the radiator 3 andmicro,-

4 phone 5 form no part of the present invention; for example, both maybe of the piezoelectric type disclosed in the copending application ofFrank Massa, Serial Number 431,429, filed February 18, 1942, andassigned to The Brush Development Company.

The radiator 3 may be sharply or broadly directional. If thektransmitted beam of supersonic waves is sharply directional, the angleover Which the microphone is sensitive may be fairly broad; if thetransmitted beam is wide, it is well to utilize a sharply directionalmicrophone. However, the bestsignal-to-noise ratio, for a given overalldirectional pattern, is obtained when-the radiator andV microphoneeachhave a pattern no broader thanthe overall pattern desired. Means (notshown) may be provided for indicating the directions of transmission andof reception, in order that bearings may be taken during the receptionof echoes.

A tunable master oscillator 9 isprovided for controlling the frequencyof the propagated compressional waves and for simultaneouslyheterodyning oscillations in the receiver 1 representative of incomingechoes.

For the purpose of causing the tuning of the master oscillator 9 toperiodically sweep-linearly over its frequency-range at a controllableperiodicity, a tunable saw-tooth oscillator Il is provided. Means I3 areprovided for adjusting the frequency ofthe saw-tooth oscillator, suchmeans, preferably being calibrated in distanceunits.

Full electronic control of the frequency of the master oscillator 9 isobtained by connecting a frequency-determining,network included therein,such as an inductor l5 and a capacitor I'l shown in Figure 2, in shuntto the anode and-cathodeof a reactance tube I 9, the input terminals ofwhich are supplied with potentials from the saw-tooth oscillator Il.

A conventional capacitive type of reactance tube. circuit is used, andthe phase shifting network consists of a gridleak 2land a capacitor 23connected between theplate and grid. The reactancefof the capacitor 23over thel frequency range covered by the master oscillator is high withrespect tothe resistance of the grid leak 2|.

Inasmuch as the oscillator ll is connected to the input circuit of thereactance tube, the mutual conductance thereof is caused to vary inaccordance with the saw-tooth'output potential. This variesthe'capacitive reactance of the plate circuit of the tubek i9 and,consequently, causes the resonant frequency of the tuned'circuit EF1-l1to also vary in the form of a saw-tooth. f

For purposes of convenient explanation,r the receiver 1 may beIconsidered as comprising a band-pass amplifier portion 25, a mixer 2l,-an intermediate frequency amplifier 29, a detector 3l and a poweramplifier 33. For the purpose of obtaining an easily observable note, anoscillator 35 is included in the receiver in the event that thetransmitted wave is unmodulated. Alternatively, an aud-io frequencymodulator 31 may be connected to the transmitter'by closing the switchV3l for the purpose of modulating the radiated pressure wave atk afrequency inthe range to which thev huma-n ear is most sensitive, forexample Y1500 cycles, in which case switch 35 is opened.

speaker or the like for giving an audiblesignal in response to thereception of an echo, or an oscilloscope may be utilized for suchindication in any indication thereof given. In the figure, the solidline designed T and H represents a propagated compressional wave thatperiodically varies linearly in frequency, under control of the sawtoothoscillator, from a lower limit of 36 kc. per second to an upper limit of48 kc. per second, and it is also representative of the oscillationssimultaneously supplied from the master oscillator 9 to the mixer 2l inthe receiver. The dotted line designated E is representative of areceived echo that lags the transmitted compressional wave by a timeinterval 75, which is the transit time or the time consumed by a givenportion of the wave train in traveling to the reflecting object andreturning to the microphone. When the lag between the radiated wave andthe received echo is exactly equal to one-half of the saw-tooth cycle,as shown, and the echo is continuous, a constant beat note of 6,000cycles is produced in the receiver. By using an intermediate frequencyamplifier 29 which is tuned to 6,000 cycles, echoes having longer orshorter transit times are rejected and do not affect the indicatingdevice 39. The system, therefore, may be said to be focused for thereception of echoes from objects at a definite distance therefrom andthe periodicity of the saw-tooth oscillator is the measure of suchdistance.

It is to be understood that the intermediate frcquency amplifier may beprovided with an adjustable selectivity control device 43, or withtunable lters or the like, whereby its selectivity is under the controlof the operator. Under conditions where considerable interference isexperisystem is increased. In other words, by sharpening thediscrimination of the intermediate frequency amplifier betwen 6 kc. andadjacent frequencies the depth of focus of the beam is decreased and thesystem becomes more and more selective for the reception of echoes fromobjects C;

lying at the exact distance away for which the saw-tooth oscillator maymomentarily be adjusted. Because of the existence of multiple reflectionpaths, however, there is a limit to the distance-selectivity that can beobtained and there is a limit also beyond which the signal-to-noiseratio cannot be improved.

'Ihe ability of the system to discriminate between echoes from objectsat a definte distance away and interfering noise also depends indirectlyupon the linearity of the frequency sweep of the master oscillator.Should the oscillator have a non-linear output it is necessary to employa more broadly tuned intermediate frequency amplier in the receiver inorder to obtain a continsystem whenan echo is beingreceived and an uousecho from the distance for which the sawtooth oscillator frequency isset, and echoes will also be received from objects somewhat closer andothers at a somewhat greater distance than that determined by theperiodicity of the saw-tooth oscillator.

The limiting supersonic frequencies, i. e., 36 and 48 kc., have been.chosen purely for illustrative purposes. The invention is not to becircumscribed by such description, however, inasmuch as other frequencyranges may be utilized.

In an alternative embodiment of the invention, instead of utilizingelectronic means forV determining the transmitting and heterodynefrequencies, certain o1 the objects of the invention may be achieved byemploying apparatus wherein the`V tuning is mechanical. For example,referring to Figure 4 of the drawings, the receiver 'l may comprise avariable input tuning capacitor indicated generally by the numeral 45, avariable heterodyne oscillator tuning capacitor 4l, and a variablecapacitor 49 may -be provided that controls the frequency range of atransmitter or of a master oscillator therefor. The several capacitorrotors may be mounted on a common shaft 5| rotated by a motor 53.

The transmitter tuning condenser is so designed that the compressionalwave emitted has a saw-tooth variation in frequency with respect totime, as indicated by the full line in Figure 5. The receiver tuning andheterodyne oscillator tuning capacitors are of the same type; the tuningof the circuits controlled thereby is indicated by the dotted line R andthe dashed line H in Figure 5. The exact design of the capacitors formsno part of the present invention; it is well known to those skilled inthe art.

In Figure 5, the tuning of the transmitter is indicated as leading thetuning of the receiver by an interval t. If such interval corresponds tothe transit time required for a definite portion of the wave train to goout and be reected from a distant object, a continuous indication willbe given of the existence of a reflecting body.

The distance to the reflecting object, therefore, is proportional to theangular velocity of the tuning capacitors and may be read from aproperly calibrated speed control device connected to the motor 53.Searching may be accomplished by varying the speed of the motor 53 untila continuous echo manifests itself. Alternatively, as indicated by thedotted arc in Figure 4, the stator 51 of the transmitter tuningcapacitor 49 may be provided with an angular adjusting device (notshown) whereby, keeping the motor speed constant, the lag t may bevaried and the distance to the reflecting object may be determined.

Also, it lies within the scope of the invention to utilize twosynchronous motors for actuation of the transmitter and receiver tuningdevices and to provide calibrated means whereby the rotor of one of themotors may be angularly changed with respect to the position of therotor of the other motor whereby the lag may be varied and observed.

The transmitter frequency range. 10,000 to 20,000 cycles per second, andthe heterodyne oscillator range, 11,500 to 21,500 cycles per second.exemplified by Figure 5, are not critical; they were chosen merely forthe purpose of providing a readily observable beat note of 1,500 cycles.

Apparatus constructed according to this invention is believed to bematerially more accurate than apparatus of analogous types heretofore 7known. -Thev accuracy may be attributedY largely tofthat characteristicof the system which enables the: searching beam of compressional wavestobe focusedf so to speak, at a deiinite distance-away, wherebyindications are vnot given of the presence of nearer or farther objects.

Other advantages of the system will be apparent toi those who arefamiliar with the art of distancemeasuring by the echo method as alsowill be numerous modifications thereof.

The invention, therefore, is not to be limited except insofaras isnecessitated by the prior artnand-by the spirit of the following claims.

We claim: Y

l. In a distance measuring system, means for producing electricalwavesatsupersonic frequencies, means for causing the frequency of said wavesto vary as a saw-tooth over a range having definite upper and lowerlimits, means for causing the frequency variation to recur periodicallyat a definite adjustable. rate, means for convertingV said electricalwaves into compressional waves in a given medium, means for receivingsaid compressional waves afterreflection from a remote object, means forconverting said received compressional waves into electrical wavesrepresentative thereof, connections for combining said representativeelectrical waves with wavesl from the first mentioned electrical waveproducing means to produce therefrom electrical waves at lowerfrequencies and means for selecting waves at substantially a singlefrequency from said last mentioned waves, said single frequency beingthe difference between either the upper or the lower limit of thefrequency Vrange and the median frequency thereof.

2. In a distance measuring system, means for producing electrical wavesat supersonic frequencies means Vfor causing the frequency of said wavesto vary asafsaw-tooth over'adefinite range having upperwand lowerVlimits, means for cause ing the frequency variation to recurperiodically ata determinable rate to focus said system sub-Vstantial-ly at a given distance, means for converting said waves intocompressional Waves in a given medium, means for receiving saidcompressional waves af-ter reflection from a remote object and forconverting them into electrical Waves representative thereof,connections for combiningsaidrepresentative waves with electrical wavessimultaneously produced by the rst mentioned means tov produce therebyelectrical waves at'vfrequencies lower than supersonic, means forselecting waves at'substantially a single frequency from said'lowerfrequency waves, said single frequency being the difference betweeneither f the frequency limits ofthe transmitted supersonic compressionalwaves and the median frequency of the range offrequencies thereof, andmeans for rendering observable said lower frequency waves whereby anindication may be had of the distance to said remote object only if saidremote object is located substantially at said focus distance.

3. In a distance measuring system, means including an electrical waveamplifier for causing compressional waves-at supersonic frequencies tobe set up in a given medium and directed toward a remote object, meansfor receiving compressionalv wavesY reflected back from said object,means'` for converting said received waves into representativeelectrical waves, a tunable master oscillator, control means for causingthe master oscillator to sweep periodically and linearly ina saw-toothrmanner over a tuning range having definiteupper and lower-frequencylimits, means for adjustingy the sweep frequency of said masteroscillator, connections for supplying oscillations fromssaid masteroscillator to said electricalwave amplifier, means for simultaneouslyutilizing oscillations from said master oscillator to produce from saidrepresentative electrical waves further electricall waves at a lowerfrequency, means for selecting waves at substantially a single frequencyfrom said lower frequencywaves, said lower frequency being thedifference between either of the frequency limits of the transmittedsupersonic compressional waves and the median frequency of the range offrequencies thereofland means for rendering said lower frequency wavesobservable, i

4. In a distance measuring system, means for amplifying electrical wavesat supersonic fre quencies, a directional supersonic compressional waveradiator connected to said amplifying means to be energized thereby, atunable source of electrical waves at supersonic frequencies forsupplying said amplifier, means for receiving compressional wavesreflected from a rem-Ote object, means for deriving electrical wavesfrom the received compressional waves, a control oscillator of thesaw-tooth type, means whereby the tuning of the tunable source is causedto vary periodically and linearly over a frequency range having an upperand a lower limit under control of the saw-tooth oscillator, means forcontrolling the period of the saw-tooth oscillator means for mixingelectrical waves from said tunable source kwith electrical wavesrepresenting received compressional waves to provide thereby electricalwaves at frequencies lower than thefrequencies of the said compressionalwaves, means for segregating from said lower frequency waves anarrowband thereof approximating in frequency the difference betweeneither of the range-limiting frequencies and the median frequency of therange, and means for producing an observable indication from said band,whereby the distance between the radiator and the wave reflecting objectmay be determined from the periodicity of the sawtooth oscillator.

5. In a distance measuring system, means of the saw-tooth type forgenerating oscillatory energy the frequency of which varies according toa linear periodic function with respect to time, adjustable means forestablishing a given period of frequency variation thereby establishinga focus distance for said system, means for transmitting a portion ofthe oscillatory energy generated to a remote object, means for receivingoscillatory echo energy from said remote object and for, derivingoscillatory electrical energy therefrom, means for combining the derivedoscillatory electrical energy with another portion of the generatedoscillatory energy to produce oscillatory beat energy having asubstantially con-r stant frequency when said remote `objectisvsubstantially' at the, focus of saidsystem and which frequency isunrelated to thedistance between said transmitter and said remoteobject, indicatf ing means, means connected to said indicating means forselecting and passing energy waves at 'substantially a single frequencywhich corresponds to said constant frequency and for rejecting all otherenergy waves whereby said indicating means indicates the presence ofsaid remote object only if it lies substantially at the focus of saidsystem, the period of variation of said oscillatory energy generatingmeans when said indicating meansv indicates the presence of a 9 remoteobject being a measure of the distance to the remote object.

6. In a distance measuring system, tunable means for generating electriccurrents at supersonic frequencies, controllable means for causing 5 thefrequency of the generated currents to recurrently vary linearly in asaw-tooth manner between predetermined limits, adjustable means forvarying the periodicity of said recurrence, means for translating saidcurrents into a train of compressional waves in a given medium, meansfor receiving said wave train after reflection from a remote object andfor deriving from said wave train electric currents representativethereof, an indicating device, means for causing the generated electriccurrents at supersonic frequencies to interact with the currentsrepresentative of received compressional waves to thereby provide abeat-frequency current for actuating said indicating device, and meanscomprising an electrical filter interposed between said indicatingdevice and said beat-frequency deriving means, said llter being tunableto pass frequencies of the order of one-half the difference between thefrequency limits of the compressional wave train to cause saidbeat-frequency current to actuate said indicating device only if saidremote object is located substantially at a given focus distance.

7. The method of detecting the presence of a 10 remote object in contactwith a given medium, that comprises continuously generatingcompressional Waves in said medium, directing said waves toward thegeneral location wherein the presence of an object is suspected,periodically linearly varying the frequency of the waves in a sawtoothmanner at a given rate between a definite upper and a definite lowerlimit, receiving compressional waves reflected from objects in the pathof the directed waves, producing from said received waves an electricalquantity representative thereof, interacting said produced electricalquantity with an alternating electrical quantity that is continuouslyrepresentative of the directed waves to thereby produce furtheralternating electrical quantities, selecting from said quantities aquantity at substantially a single frequency which is substantiallyequal to half of the difference between the frequency limits of therange of variation of the directed-wave frequencies, providing anindication of the distance to an object by observing the rate at whichthe compressional waves vary between the set denite upper and lowerlimits, and selectively changing said rate whereby the focus of saidsystem is changed.

WALTER. J. BROWN.

JOHN E. SHOMER.

Disclaimer 2,405,134.-`Walter J. Brown, Cleveland Heights, and J 07m E.Simmer, Lakewood, Ohio. DISTANCE MEAsUmNG SYSTEMS. Patent dated Aug. 6,1946. Disclaimer filed May 18, 1959, by the assignee, UlevzteO'orporation. Hereby enters this disclaimer to claim 5 of said patent.

[077czal Gazette July 7, 1959.]

Notice of Adverse Decision in Interference In Interference No. 84,436,involving Patent No. 2,405,134, l/V. J. Brown and J. E. Sholner,Distance measuring systems, final judgment adverse to the patentees wasrendered March 27, 1959, as to claim 5.

' [Official Gazette October 13, 1959.]

